Energy conservation has become a major concern in the design of electrical circuits and systems. Energy conservation has benefits to the end users and society as a whole. For example, on the one hand, diminished use of energy lowers operating costs of the system. On the other hand, diminished need for energy results in diminished adverse environmental impact such as pollution, depletion of resources and the like. One example of the need for reduction in energy consumption lies with the operation of AC motors. The use of such AC motors has become commonplace. Many ordinary appliances and much of the equipment used in residential as well as in industrial and commercial settings utilize such motors. These motors are ordinarily connected to power lines provided by local utility companies, which can vary substantially in voltage between locales and over time. Motors typically operate at relatively constant speeds, the speed being independent of the applied AC voltage to the motor over a range of operating voltages.
The energy consumption of any load element in an electric circuit, such as a motor, is determined from the integral over a predetermined period of the product of the instantaneous AC voltage applied across the load terminals and the instantaneous AC current through the load. Typical AC line voltages are sinusoidal. It is known that applying a sinusoidal input to an inductive load will result in both the AC voltage and AC current having the same sine wave shape but with an offset in time. The time offset between voltage and current is called a phase shift or phase difference and is typically expressed as an angle. For a constant voltage and, hence, relatively constant current, the power consumed by a load may be expressed as VIcos.PHI., where V is the average value of the applied AC voltage across the load, I is the average value of the AC current through the load and .PHI. is the phase difference between the voltage and the current. Cos .PHI. is sometimes referred to as the "power factor". Thus, power consumption is related to the phase difference between the AC voltage applied to the load and the AC current through the load. This phase difference is dependent upon the load condition of the motor. Hence power consumption is dependent upon the load status of the motor and upon the line voltage applied to the motor.
Most motors are designed to operate adequately at predetermined line voltages. Normally, the motor designer must assume that the motor will be operated at the lowest line voltage normally encountered. Such a voltage may be far lower that the normal line voltage available at most locations and at most times. For example, a load used in a refrigerator must be capable of delivering adequate power under full load during a "brown-out" condition, i.e., when a utility reduces line voltage over its entire grid (or portion thereof) in response to unusually high electrical energy demand. Changes in line voltage effects both load performance and energy consumption. While wide variations in line voltage are, thus, undesirable, such variations are beyond the control of most load designers and users. It is noted that ordinary line voltage fluctuations will not result in changes in the phase between the current and the voltage. Prior art energy conserving systems are responsive to changes in phase but not to fluctuations in line voltage.
Therefore, there is a need for a energy savings system for controlling the voltage applied to a load which is simple and which is responsive to changes in line voltage to adjust for such changes.
Accordingly, it is an object of the present invention to provide an improved load control system for energy savings.
Another object of the invention is to provide an energy savings system for use with various loads which are simpler in design than the prior art.
These and other objects of the invention will become apparent to those skilled in the art from the following description and accompanying claims and drawings.